No, it really isn't. Certainly they deal with many of the same themes, and if you want to say that Haldemann does a much better job then I can probably agree with that, but accusing Ender's Game of being a mere rip-off just because they address similar topics is silly.
(OSC is also a weird and outspoken homophobe; easy to see him (a) misunderstanding forever war and (b) liking it for the wrong reasons).
Look, card is clearly the better writer between the two of them. He added a lot. But if you want to put forward war fiction as a case for empathy, it's irresponsible to look at EG before FW.
https://en.wikipedia.org/wiki/Ender's_Game#Creation_and_insp...
> Ender's Game was written specifically to establish the character of Ender for his role of the Speaker in Speaker for the Dead, the outline for which he had written before novelizing Ender's Game.
The continuation of enders war do go into much more societal factors.